;286 Rafinesque on a fossil Medusa. 



well known that the animals of that tribe are of a soft gela- 

 tinous substance and structure, they do not leave any exuviae 

 after their death, and they are very easily destroyed by the 

 contact of any hard substance, whence it is no wonder that 

 their fossil remains are so rare : yet in the specimen under 

 consideration, the animal appears quite perfect, and is em- 

 bedded in a crystallized limestone ; the mode of its fossili- 

 zation is therefore very singular. We must either suppose 

 that this extinct species was of a harder cartilaginous sub- 

 stance, or that the liquid in which it was swimming or floating, 

 was coagulated at once : it even appears probable to me that 

 both circumstances may have occurred, since the specimen 

 is in its proper natural position, and not in the least com- 

 pressed nor altered ; but the whole of it is changed into a 

 similar stone to that which surrounds it : the animal howev- 

 er is become rather silicious as usual with fossil mollusca 

 or polyps. 



Genus Trianisites. — (See the engraved figure.) 



Generic definition. — Body with three unequal peduncles 

 or appendages underneath, the middle one with a mouth or 

 opening at the extremity, surrounded by two fascicles of 

 short tentacula. Back simple, not ombrelled. 



Generic ohservations. — The generic name derives from 

 Greek words meaning, three unequal appendages. In the 

 natural arrangement this genus will belong to the real family 

 medusa, and to the sub-family hranchypia, having peduncles 

 or appendages underneath and no wing nor bladder on the 

 back, next to the ^ewns pelasgia of Peron and Lesueur; but 

 it differs from it, and indeed from any other of that tribe, 

 by having a sort of trifid body, and the tentacula only near 

 the mouth. The following species is the type of the genus. 



Trianisites Cliff or di. 



Specific definition. — Back subconical and subacute, axil- 

 las obtuse and unequal, peduncles compressed transversally 

 obtuse, the shortest larger, the longer one smaller and op- 

 posed to it, the middle one nearly as long, extremity fim- 

 briated by the tentacula. 



